1. Field of the Invention
The invention relates in general to a method for fabricating a liquid crystal display (LCD) panel, and more particularly to a method for fabricating an LCD panel with Gamma correction function.
2. Description of the Related Art
Referring to FIG. 1, a diagram showing the optical transmittance of conventional pixel components corresponding to RGB illuminators under different drive electrical fields is shown. The horizontal coordinate corresponds to the electrical field strength, and the vertical coordinate corresponds to the optical transmittance. The liquid crystal molecules have different degrees of refractivity and retardation towards visible light of different wavelengths. Therefore, when driven by the same strength of electrical field, the conventional pixel components have different transparencies corresponding to RGB illuminators.
Normally, Gamma curve is used to quantity a viewer's visual perception in the design of LCD monitor circuit. Gamma curve describes the relationship between the photo-transparency of a liquid crystal layer and the corresponding luminance perceived by the viewer. The luminance perceived by the viewer is inferred from the driving electrical field strength of the liquid crystal layer. FIG. 2 is a diagram showing the Gamma curves of a LCD monitor corresponding to the relationship between the electric field and the transmittance in FIG. 1. The horizontal coordinate corresponds to color level number, while the vertical coordinate corresponds to the optical transmittance. As shown in FIG. 2, the Gamma curves for the red light, the green light and the blue light are different and separate. This implies that when the electrical fields of the same strength are provided to the liquid crystal layer, the luminance of the red light, the luminance of the green light and the luminance of the blue light cannot maintain a constant ratio, and would deviate from the predetermined white balance of the LCD monitor. Consequently, bias would occur between the display colors as viewed by the viewer and the display signal as inputted.
The method to resolve the above problem can be categorized into two aspects: the circuit and the structure. In terms of structure, the typical method is to change the electric field strength applied to the liquid crystal layers of different color pixels by directly adjusting the thickness of the liquid crystal layer which is disposed inside the LCD monitor and corresponds to the display of the RGB pixels. Referring to FIG. 3, a cross-sectional view of a conventional LCD monitor is shown. In FIG. 3, a liquid crystal layer 110 is formed between a first substrate 102 and a second substrate 104. Moreover, three transparent organic layers 112R, 112G and 112B of various thicknesses corresponding to pixels of different colors are respectively disposed on the top surface of the first substrate 102, while three color filters 108R, 108G and 108B corresponding to pixels of different colors are disposed on the bottom surface of the second substrate 104. The pixel electrode 106 of the RGB pixels is disposed on the top surface of the above transparent organic layers 112R, 112G and 112B, and a common electrode 120 is disposed on the bottom surface of the color filters 108R, 108G and 108B, so as to generate a driving electric field E in the liquid crystal layer 110. Besides, two alignment films 130 and 140 are respectively disposed on the surface of the common electrode 120 and that of the pixel electrode 106 for the alignment of the liquid crystal layer 110.
It is noteworthy that the transparent organic layers 112R, 112G and 112B are different in thickness, causing the corresponding liquid crystal layer 110 to have different thickness and the corresponding driving electrical field to have different strength in consequence. It can be seen from the above disclosure that by adjusting the thicknesses of the above transparent organic layers 112R, 112G and 112B, the strength of the driving electric field is changed, the alignment of the liquid crystal molecules in the liquid crystal layer 110 is adjusted, the optical transmittance of the liquid crystal layer 110 is changed, and finally the object of calibrating and separating the RGB Gamma curves is achieved.
However, the above solution still has the following disadvantages:
1. An extra manufacturing process of fabricating the transparent organic layers 112R, 112G and 112B is required prior to fabricating the pixel electrode, resulting in an increase in terms of manufacturing cost and manufacturing time.
2. The transparent organic layers 112R, 112G and 112B have different thicknesses in respective positions corresponding to the pixels of different colors, resulting in a bumpy surface of the transparent organic layers, making it more difficult in forming the alignment film 140 on the surface of the pixel electrode 106 in subsequent liquid crystal alignment process.
3. The pixel electrode 106 covers the bumpy surface of the transparent organic layer 112R, 112G and 112B. Since the transparent organic layers 112R, 112G and 112B of different colors have different thicknesses, a horizontal electric field occurs between adjacent pixels electrodes 106 of different colors, and the alignment of the liquid crystal molecules and the normal operation of the liquid crystal layer 110 would be affected.